Mosquito research in Barton Hall

RON HOY: Well, as you can see around us, here we are in beautiful Barton Hall. I've been to many field sites in my almost two score years of research. This is definitely one of the most exotic field sites with that we've done any acoustics in.
Now you may wonder, why in the world would anybody be doing auditory neurophysiology in a field house. Well, we're doing so because we're in Ithaca. And we can't be in a real field.
I mean, for heaven's sakes, it's 11 degrees out there. And we're working with mosquitoes. And they would last about oh maybe a minute and a half, and they'd be frozen. So we're here because we need a clear, clear field for sound to travel so that it's not going to bounce off of walls and the like, which of course in any normal laboratory would be a problem.
But here, we have more than 10 feet. We've got 20-30 feet. And so we've got a nice, clear, free field for sound to travel through before, and unimpeded, so there's no bouncing.
I mean, you might think that, oh well, wait a minute. Don't you need a carpeted floor? Well, guess what? We have a carpeted floor.
And people worry about ceilings. Well, we're talking about 100 feet. So that clearly is not going to be a problem.
In many ways, we couldn't have asked for something better. Of course, a nice clear pampas in Argentina might be nice. But this is going to do.
And the reason that we're doing this experiment is to follow up on an observation that Gil Menda made when he had an electrode in the auditory nerve of the mosquito. And what happened there was that he observed that the auditory neurons were responding to other people in the lab talking. And that's sort of absurd because we think of a mosquito acoustic sense in terms of vibrations.
But if you're more than a few feet away, you're in the sound field. And so that raises a very interesting question. Why would a mosquito be hearing sound?
Well, Laura Harrington will tell you about the particular mosquito that we're working with tends to congregate, males and females, around a host. That host happens to be people, just like you and me. And well, what are the sorts of cues that people give off? Well, of course we give of chemical cues-- CO2, heat. But more than anything else, we're always talking. And so that's the far-fetched-- the blue-skies, so to speak-- reason for doing this experiment.
And I think Laura can talk a little bit more about the natural history of the mosquitoes.
LAURA HARRINGTON: Well, that's a really good question. And I think for a long time, many scientists have assumed that they don't care about sound. But recently, we have some preliminary results which indicate that they hear from much farther away than previously thought. And it actually makes sense.
So we're working with a mosquito called the Aedes aegypti. Its common name is the yellow fever mosquito. It's common throughout the tropical regions of the world. And it's the most important mosquito vector of viruses that affect humans.
So it transmits dengue. It transmits chikungunya virus. It's a day-active mosquito, which is a little bit different than most mosquitoes.
So it's active during the day. It probably uses different types of cues to find its host than night-active mosquitoes. And it makes sense to us that they're probably hearing each other. We already know that from mating. But also, there's a chance they're hearing their hosts, as well.
GIL MENDA: So the first step is to harness the mosquito in a way that it will be not mobile, and there will be no movement artifact. And it's going to be easier to do all-day neurophysiology with them. So to do so, I have a dose-- a 200-microliter pipette tip that I used before for restrain fruit flies. And I also used the same thing to restrain the mosquitoes.
And the important part is to cut the tip in a diameter that will fit to the size of the thorax of the insect that we're using. I go into the suction. So I have this kind of a tube. I attach it here. And then I have a lot of mosquitoes here.
So you can see, this is the containers with all the mosquitoes. This is just to keep them humid so they will have water. And you can see all the males here.
Now I just going to go gently inside and suck one male inside. The difference between the male and the female is that the males are a little bit smaller and got a very feathery-shaped antennas. And so you can see it's pretty nice. And over here, we have 95% males in this cage.
So I just try to suck one. OK. You can see it inside here. He's already kind of almost at the entrance.
And I need to push him. So I do the pushing under the microscope because I have to be very gentle not to kill him. So right now, what I going to do is just take that antenna out because it's kind of stuck below.
And you can see he's active. So if I will take some honey, I will show you. It's pretty cute. You can see that he's feeding now.
I have to glue his proboscis down. That's what hold the head. And there is no movement artifact of the mosquito trying to reach for food or something like that.
What you're going to see now is that I have two electrodes. I have one electrode and one ground. The ground I plug in to the thorax.
People ask me many times, say, it's such a small brain. How can you go to the brain? I mean, we're talking about less than a millimeter, like a few hundred microns. And under the microscope everything look big.
[STATIC]
[MAGNIFIED VOICES]
The blue channel represent the mosquito. And the green channel represent the microphone detecting my sound. In this case, my sound later on the tone the two played.
[INCREASINGLY HIGH-PITCHED TONES]
So what's known by now is that mosquito hear with their antenna. So the antenna is responding to particles. And every tiny movement of the antenna is being sensed in the gel. It's the ball that hold the antenna.
And inside that ball, there are like, in each antenna, there is like 7,500 of the receptor. Just to compare it for humans, we have in each ear approximately 2,000 receptors. And mosquito, it's such a small insect, got in one gel 7,000. So it's very, very sensitive.
What was important for us is to see if the mosquitoes can hear from a distance that will be more in the range of a far field and away from the near field area known until now that mosquito can hear. So we know that mosquito can hear from a very close distance-- around 10-15 centimeters, maybe a meter if we are talking about low frequencies. This is like the lengths of the sound wave.
But in Barton Hall, we needed a big space with no obstacles in the way that we can see if the mosquito can hear far field. And what we learned that in our case, we just measure it 10 meters away from the mosquito. And we learned that the mosquito can sense the different kind of frequencies that we tested very well.
So that's, for us, it's the first step of proving that mosquito can hear up to a far field. The sound that we played, it was approximately a human speech from 10 meters away. So we found that a mosquito can hear between-- the response was between 70 dB to 80 dB. And this is kind of a nice conversation between humans at approximately the range of a intensity.

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Barton Hall is used for many things: athletics, concerts, giant dinners, final exams. But mosquito research? Professors Ron Hoy (neurobiology and behavior) and Laura Harrington (entomology), together with a group of students and postdocs, took over Barton Hall for one night to test the hearing of mosquitoes. This film describes the process and the rather surprising result of their experiment.